Power assist servosystem



Oct. 23, 1962 R. E. TOMEK 3,069,360

POWER ASSIST SERVOSYSTEM Filed Dec. 1'7, 1959 2 Sheets-Sheet 1 INVENTORReinhold E. Tome/r m, Kim, 1% M [w ATTORNEYS Unite States This inventionrelates to improvements in follow-up devices or automatic controlsystems of the torqueless and frictionless type. More particularly, thisinvention relates to a control system utilized as a shaft coupling forpositioning an output member in response to the position of an inputmember without using any of the torque of the input member, the controlsystem characterized by the absence of any false stable null position.

In many fields of present day endeavor it is necessary to follow-up theposition of an input member because the input member has very littletorque applied to it to directly drive an output member. For example, inairborne and other data-handling systems, emphasis is being placed onsource digitizing, i.e., converting a transducer output directly to adigital number by means of a digital converter. Since some types oftransducers inherently possess very little output torque, specialconsiderations must be made for coupling the transducer to a digitalconverter. That is, with practically no input torque a coupling must bedevised which will provide output shaft positioning and suitable outputtorque.

One solution to this problem is an automatic follow-up system used as acoupling. Some of these systems, using optical means, can operate tofollow the movement of an input rotary member with no torque being takenfrom the input member.

Various systems are known in the prior art wherein light-sensingphotocells are utilized in a follow-up system. However, one of thedifiiculties of the prior known systerns is the fact that they possess astable false null. in other words, at a position 180 from the true nullposition the device will stabilize at a false null. This of course willproduce a false output causing the follow-up device to stabilize theoutput position diametrically opposite the input position. Accordingly,it is the principal object of this invention to provide a torquelesscoupling device for causing an output member to follow an input memberby means of a follow-up system which is responsive to a radiation sourceand which will possess no stable false nulls.

It is an additional object of thi invention to provide a coupling forfollowing the movement of an input member when the input memberpossesses little torque and none of this torque is utilized in thefollow-up system, the coupling also being brushless and extremelycompact.

These objects are accomplished in a torqueless coupling having no stablefalse nulls, by providing the coupling with a radiation source and apair of oppositely monitored radiation-responsive devices connected incircuit to a reversible electric motor which positions an output member.An input member drives a pair of partial radiation blocking disks formetering the radiation from the radiation source to theradiation-sensitive devices and the output member also drives a pair ofpartial radiation blocking members such that movement of the inputmember will cause a greater radiation reception at one or the other ofthe oppositely monitored radiation-responsive devices in accordance withdirectional movement of the input member, and the motor in responding tothe radiation reception will drive the output member toward the stablenull position.

Other objects and advantages of the invention will be pointed out in thefollowing description and claims and v illustrated in the accompanyingdrawings which disclose,

"ice

by way of example, the principle of the invention and the best modewhich has been contemplated of applying that principle.

In the drawings:

FIG. 1 is an exploded view of the mechanical components of thetorqueless coupling of this invention;

FIG. 2 is a schematic illustration of the coupling of this invention ina balanced or null position;

FIG. 3 i a schematic illustration of the coupling of this inventionafter the input shaft starts to rotate clockwise;

FIG. 4- is a schematic illustration of the coupling of this inventionafter the input shaft starts to rotate counterclockwise;

FIG. 5 is a schematic illustration of the coupling of this inventionshowing the position at a false null and how such position is unstable.

In general, the torqueless coupling of this invention contemplates atleast one radiation source such as balanced light for directing lightequally toward a pair of oppositely mounted photocells or otherradiation-responsive devices. An input shaft and an output shaft areaxially aligned and the input shaft drives a pair of partially opaquesectored disks attached thereto. One of these disks is on one side ofthe central light source and the other disk is on the other side. Eachdisk serve to partially block the light radiated toward each of thephotocells. The output member likewise drives a pair of partially opaquesectored disks and each one of these disks is similarly positioned onopposite sides of the light source to partially block the response ofthe photocells. The arrangement is such that by rotating the input shaftin one direction, one of the photocells produces an output greater thanthe other and this net output is fed to a DC. amplifier and then to areversible servomotor to rotate the output shaft and thereby move thepair of sectored disks connected thereto to a position angularlycoinciding with the input shaft position to again balance the responseon the photocells. At a stable null position a very small amount oflight reaches each photocell and the small voltage generated is the samefor each photocell, thus the system is balanced. When the input isrotated from its stable null position, full light will reach each of thephotocells and the system will be momentarily balanced at a false nullposition. However, by moving the input or output shaft only slightlyfrom this false null one of the photocells receives more light than theother. This net output from the oppositely monitored photocells willcause the reversible motor to drive the output shaft in a directionopposite to the input shaft rotation causing the balanced stable nullposition to be again obtained.

Referring now to the drawings, FIG. 1 is an exploded perspective view ofthe torquelesscoupling of this inven tion. As shown in FIG. 1, abalanced light source 10, which may consist of a plurality of electriclamps 12 and a pair of frosted glass covers 14 and 16 within acylindrical upport housing 18, is provided. The balanced light source 10is adapted to provide approximately the same amount of'light from eachside thereof. A pair of split covers 20 and 22 are attached to the lightsource housing 18. The attachment may be by suitable screws 24 and 26 orthe like.

A radiation-responsive device such as a voltage generating photocell 28and 30 is positioned within each split cover. An input shaft 32 isjournalled in a bearing 34 in cover 20, and a pair of partially opaquesectored disks 36 and 38 are rigidly secured to the shaft 32. Disk 36 ispositioned between balanced light source 10 and photocell 28, while disk38 is positioned between balanced light source 10 and photocell 30. Disk36 has a quarter sector 37 which is transparent and a three quartersector 39 3 which is opaque. Disk 38 is half transparent at 35 and halfopaque at 41.

An output shaft 42 is journalled in a bearing 71 in cover 22, and isrigidly connected to a disk 44. The disk has an opaque area 43 and atransparent area 45 similar to disk 36. A transparent coupler member 46is rotatably journalled on input shaft 32 by suitable bearings 48 andhas a collar extension 50 extending from one side thereof through thelight source housing 18 and journalled therein by bearing 70. A pair oflugs 52 extend longitudinally of the axis of the coupler to co-operatewith notches 54 in disk 44 to establish a driving connection between thecoupler 46 and the disk 44. The collar 50 of coupler 46 is likewiserigidly connected to a disk 56 by means of a key 63. Disk 56 is alsohalf opaque 55 and half transparent 57 similar to disk 38. it can beseen with this arrangement that the input shaft 32 drives disks 36 and38 directly to partially block the light from light source directedtoward both photocells 28 and 30. In a similar manner output shaft 42directly drives disks 44 and 56 to also partially block the lighttransmitted from light source 10 to both photocells 28 and 3t Thus, thedisks are, in effect, light shutters. By the arrangement of one disk ofeach connected set being on opposite sides of the light source theangular movements of the disks control a bi-directional independentresponse, e.g., if disk 36 is moved to allow more light to photocell 28disk 38 is moved in a direction which will not affect the response ofphotocell 30.

As shown in FIGS. 1 and 2, the opaque and transparent areas of thesectors are arranged such that at the true null position, shown in FIG.2, the small amount of light transmitted to each photocell balances thesystem. The photocells are oppositely monitored or oppositely connectedin the circuit, for example, photocell 28 may produce a positive outputvoltage to a DC. amplifier 60 while photocell 30 may produce a negativevoltage to the amplifier. A reversible servomotor 70 is driven by theoutput of DC. amplifier 60 and motor 70' is mechanically coupled to theoutput shaft 42 by a suitable connection 72. As can be seen from FIG. 2,at the true stable null position the sectors 56 and 36 meter theradiation from light source 10 to photocell 28 and similarly sectors 38and 44 meter the radiation from light source 10 to photocell 30. Withequal reception of a small amount of light the net output of these cellswill be zero, i.e., the response will be balanced, and the output shaftwill then be positioned according to the angular position of the inputshaft.

FIG. 3 illustrates the condition of the device when a clockwise movementis applied to the input shaft. When this happens, the sectored disks 36and 38 rotate clockwise and the transparent area 37 of disk 36 combinedwith the transparent area 57 of disk 56 allows increased radiation fromlight source 10 to energize photocell 28 while the light to photocell 30remains blocked producing a net positive voltage to the DC. amplifier 60causing the motor 70 through its mechanical connection 72 to rotate theoutput 42 clockwise. Rotation of the output shaft clockwise drives disks44 and 56 clockwise, the opaque area 55 of disk 56 gradually cutting offthe light transmitted from light source 10 to photocell 28 until abalanced stable null condition is again obtained. At this position theoutput shaft 42 has moved clockwise to an angular position coincidentwith the angular position of the input shaft 32.

FIGURE 4 illustrates the device when a counterclockwise movement hasbeen applied to the input shaft 32. This counterclockwise movementcauses the transparent area 35 of disk 38 to allow increased light topass from light source 10 through transparent area 45 of disk 44 ontophotocell 30, thus producing a net negative voltage to DC. amplifier 60,causing reversible servomotor 70 to rotate the output shaft 42 throughconnection 72 in a counterclockwise direction. This counterclockwisemovement causes the opaque area 43 of sector disk 44 to move into thepath of light falling on photocell 3t) and gradually cut it off,approaching a balanced stable null condition. Should the inertia of thesystem carry the output shaft beyond this point, the light response ofthe positively monitored photocell 28 will increase, driving the outputshaft in a clockwise direction until the stable null is reached.

FIGURE 5 illustrates the input shaft 32 at a false unstable nullposition 1 opposite the stable null position. At the false nullposition, it can be seen that maximum light is transmitted from lightsource 10 to both photocells 28 and 30 and the net output to theamplifier 60* is zero. However, the quarter sector transparent area ofdisks 36 and 44 does not allow the light to saturate the photocells 28and 30'. That is, the exposure of both photocells to maximum light willstill allow reductions in the light shutter openings to effect thevoltage output of the photocell. If maximum light were to saturate thephotocells the unstable null condition could exist for small rotationaldeviations from this condition since no net output voltage variationwould exist. A saturation condition can be prevented by changing maximumallowable shutter opening or by a diminishing light source, preferablythe latter.

With the coupling at a false null position wherein maximum light willnot saturate the photocells, slight movement of the input shaft 32 ineither a clockwise or counterclockwise direction will diminish theoutput of one or the other of the photocells producing a net output toamplifier 60. For example, from the unstable false null position anymovement of the input shaft 32 in a clockwise direction will cause thelight transmission from source 10 to the photocell 28 to decrease, whilemaximum light is still reaching photocell 30. This provides a netnegative output fromthe combined photocells to the DC. amplifier 60,driving the output shaft 42 from the motor 70 in a counterclockwisedirection which in turn further increases the net negative output,causing shaft 42 to continue to be driven with increased rapidity in acounterclockwise direction for until the balanced stable null isreached. In other words, when moving from an unstable false null to astable null position one photocell continues to see maximum lightthrough a transparent quarter sector and the light to the otherphotocell is diminishing. Therefore the motor 70 will drive the outputshaft 42 with increased rapidity toward the stable null position.

Applicants invention thus essentially includes the oppositely monitoredphotocells for causing a reversible motor to rotate in oppositedirections to position an output shaft in combination with partiallyopaque and partially transparent inline rotatable disks connected inpairs to the input and output shafts. By having one disk of eachconnected pair on each side of the light source as control shutters foroppositely monitored photocells, each disk pair effectively rotates inopposite angular photocell response directions such that one disk ofeach connected pair is affecting light reception at one photocell morethan at the other photocell. This situation is accomplished only byhaving one disk of each pair between the light source and eachoppositely monitored photocell and having a pair of disks connected toboth the output and input shafts.

As can be seen from the foregoing, applicant has disclosed a compacttorqueless coupling possessing no stable false nulls and utilizingin-line partially opaque sector disks. It should be pointed out that theopaque and transparent areas of the disks are arbitrary and otherconfigurations of opaque and transparent areas could be utilized toproduce the same results. Also, although an electric light andcurrent-generating photocells have been utilized as the source andsensing means, other sources and sensing means known in the art arecontemplated. For example, any source of radiation and any pair ofoppositely monitored radiation-responsive devices with means forblocking the radiation similar to the disks illustrated in the preferredembodiment could be utilized.

While there have been shown and described and pointed out fundamentalnovel features of the invention as applied to the preferred embodimentit will be understood that various omissions and substitutions andchanges in the form and details of the device illustrated and in itsoperation may be made by those skilled in the art without departing fromthe spirit of the invention. It is the intention, therefore, to belimited only as indicated by the scope of the following claims.

What is claimed is:

l. A torqueless coupling comprising; at least one radiation source, apair of radiation responsive devices, a reversible motor, meansconnecting the radiation responsive devices to the reversible motor suchthat when one of the radiation responsive devices receives moreradiation than the other one the motor will rotate in one direction andwhen the other radiation responsive device receives more radiation thanthe first one the motor will rotate in the opposite direction, a rotaryinput shaft, a separate rotary output shaft, a driving connectionbetween the output shaft and the reversible motor, a pair of memberspartially opaque and partially transparent to transmitted radiationconnected to the input shaft and another pair of similar membersconnected to the output shaft, one of each pair of the members beingpositioned between the radiation source and one radiation responsivedevice to partially block the response of each radiation responsivedevice from the radiation source such that the movement of the inputshaft in either angular direction will thereby vary the response of theradiation responsive device due to movement of the opaque andtransparentareas on the partially opaque and partially transparent members and thisvariation in response will cause the reversible motor to drive theoutput shaft in a direction to cause the response of the radiationresponsive devices to balance at a stable null position when the outputshaft is angularly referenced to the input shaft.

2. A torqueless follow-up control system comprising; a light source, apair of oppositely monitored light sensitive devices, a pair of separaterotary systems, each of said rotary systems connected to a pair ofpartially opaque, partially transparent members, a member of each rotarysystem being interposed between said light source and one of said lightsensitive devices, whereby a pair of partially opaque, partiallytransparent members, one connected to each separate rotary system willbe interposed between said light source and each light sensitive device,the opaque and transparent areas on each mem ber being arranged to allowonly a small amount of light from the light source to reach said lightsensitive devices when the separate rotary systems are angularlyaligned, and when the separate rotary systems are angularly offsetallowing light to reach separate light sensitive devices depending uponthe direction of angular offset, and a reversible motor operativelyconnected to one of the separate rotary systems for rotating the systemand bring it back to a condition of angular alignment, the motor beingcontrolled by the response of the light sensitive devices.

3. A torqueless coupling connecting an input shaft to an output shaft tocause said output shaft to move the same amount and in the samedirection as the input shaft, said coupling comprising; a reversibleelectric motor connected to drive the output shaft, a source of light, apair of oppositely monitored photocells, electrical connections betweensaid photocells and motor for driving said motor in a directiondepending upon the output of the photocells, a pair of disks between thelight source and each photocell, one of said disks of each pairconnected to the input shaft and the other being connected to the outputshaft, means defining opaque and transparent areas on said disks suchthat when the input shaft position and output shaft correspond at astable null position each photocell has an equal response and when theinput shaft is moved in either direction the movement of the connecteddisks allows the net output of said photocells to increase to drive themotor selectively in either direction, the parameters of the lightsource and the opaque and transparent areas on the disks being such thatat maximum light reception the photocells will not be saturated, thefalse null position diametrically opposite the stable null positionbeing unstable due to any slight movement of the input or output shaftproducing an unbalance in the reception of the photocells producing anet output and causing the motor to drive the output shaft back to thebalance stable null position.

4. A torqueless coupling as defined in claim 3 wherein the source oflight, the photocells, the input and output shafts, and the diskscarried by the input and output shafts are axially aligned.

5. A torqueless coupling as defined in claim 4 wherein the axiallyaligned components are enclosed in a. compact cover member totallyenclosing said components with the exception of extensions of the inputand output shafts, and bearings being carried by said cover member forjournalling the input and output shafts.

6. A torqueless coupling as defined in claim 5 wherein the pair of disksconnected to said output shaft are connected together by means of atransparent mechanical coupling member, the coupling member beingrotatable on the input shaft and having axial extensions rigidlyconnected to each of the disks on the output member.

7. A torqueless coupling as defined in claim 5 wherein the opaque andtransparent areas on the disks are sectors of a circle, one disk of eachpair being a half sector opaque and a half sector transparent while theother disk of each connected pair being one quarter transparent andthree quarters opaque in sectors.

8. A torqueless coupling comprising; an input shaft and an axiallyaligned separate output shaft, a split housing, each half of said splithousing containing a bearing for journalling each of said shafts, abalanced light source positioned substantially in the center of thehousing to direct light in opposite directions of equal intensity, apair of oppositely monitored photocells positioned in each end of saidsplit housing on opposite sides of said balanced light source, areversible electric motor operatively connected to drive the outputshaft, electrical connections between said oppositely monitoredphotocells and said motor for driving said motor in the directiondepending upon the response of the photocells and the net outputtherefrom, a pair of disks rigidly connected to said input shaft, one ofsaid disks being on each side of said balanced light source, a diskrigidly connected to said output shaft and positioned thereon betweenthe balanced light source and the photocells, a coupler unit journalledin a bearing in said balanced light source housing and rigidly connectedto saiddisk on the output shaft, another disk rigidly connected to saidcoupler and positioned between said balanced source and the otherphotocell, means defining opaque and transparent areas on said diskssuch that when the input shaft position and output shaft positioncorrespond a balanced stable null position is reached with eachphotocell receiving equal response from the light source, and when theinput shaft is moved in either direction relative to the output disk,the connected disks allow the response of the photocells to thetransmitted radiation from the balanced light source to vary in adirection which will cause the reversible motor to drive the outputshaft back to the stable balanced null position, the parameters of thelight source and the opaque and transparent areas on the disks beingsuch that at maximum light reception the photocells will not besaturated, whereby a false null position diametrically opposite thestable null position will be unstable due to any slight movement of theinput or output shaft causing the motor to drive the output shaft withincreased rapidity back to the balanced stable null.

9. A power assist servosystem comprising; at least one radiation source,a pair of radiation responsive devices, a drive means having areversible output and the drive means being operatively connected to theradiation responsive devices such that when one of the radiationresponsive devices receives more radiation than the other one thereversible output of the drive means will move in one direction and whenthe other radiation responsive device receives more radiation than thefirst one the reversible output of the drive means Will move in theopposite direction, a rotary input system, a separate rotary outputsystem, an operative connection between the out put system and thereversible output of the drive means, a pair of members partially opaqueand'partially transparent to transmitted radiation connected to theinput system and another pair of similar members connected to the outputsystem, one of each pair of the members radiation responsive device topartially block the response of each radiation responsive device fromthe radiation source such that the movement of the input system ineither angular direction will thereby vary the response of the radiationresponsive device due to movement of the opaque and transparent areas ofthe partially opaque and partially transparent members and thisvariation in response will cause the reversible output of the drivemeans to drive the output system in a direction to cause the response ofthe radiation responsive devices to balance at a stable null positionwhen the output system is angularly referenced to the input system.

References Cited in the file of this patent UNITED STATES PATENTS

